The invention relates to solid detergents. The invention relates more specifically to solid detergents having enzymes and stable oxygen-releasing bleaching agents that are stable upon storage of the detergent.
Detergent systems for laundry, warewashing, hard surface cleaning (food plant, institutional, industrial, transportation), and numerous other similar applications have long been available where powders are manually scooped into water and dissolved. The resulting detergent solution is applied to the surface or article being cleaned. Also, concentrated liquid detergents have been found to be highly desirable by certain consumers. Important considerations in the selection of a detergent composition include ease of handling, cleaning ability and stability of the product during storage. The basic ingredients of a detergent are surfactants, which emulsify and suspend soils, and alkaline builders, which saponify fats and oils.
One advantage of powder detergents is the high concentrations of active ingredients because few or no inert ingredients are required. In powder detergents, high levels of inorganic or organic salts can be used to raise alkalinity and soften water by chelating or sequestering water hardness ions. The powdered detergents can be used to provide oxidizing agents (bleaches) or reducing agents (for example, sodium thiosulfate) and granular enzyme materials which can be blended into free flowing powder detergents. The oxidizing or reducing agents and the enzymes are stable in the powdered detergents with no significant loss of activity on extended storage.
A significant disadvantage of powder or granular detergents for commercial applications is that they are not as accurately controllable in dispensing equipment as liquids. Powder systems can require manually scooping a quantity of powder for each use, thus not taking advantage of the ease, accuracy and hands-off labor savings of liquid dispensers. Also, powders can cake if exposed to high humidity or temperatures. Once they become caked, they cannot be subsequently removed from their shipping container. Powders can lose some of their activity if moistened or exposed to high humidity. Non-homogeneous powders can segregate in their shipping containers, that is, separate or stratify by particle size or density resulting in a non-uniform mixture that may not be appropriate for ultimate use applications. Furthermore, powders can create a safety hazard in that granules or airborne dust particles of irritating or corrosive materials can exit their container or otherwise come in direct contact with tissue causing burns or discomfort.
To improve handling and dispensing, free flowing powder detergents or tacky bulk powder detergents have been poured from premeasured packets or scooped from drums into convenient sized dispensers with a relatively fine mesh screen holding the powder above a spray nozzle. To deliver the detergent from the dispenser, water sprays through the screen to dissolve the powder with the resulting solution or slurry being delivered to the use site or a suitable container. Use of the screened off dispenser allows the utilization of the powder detergents in commercial applications with some of the dispensing advantages found with liquids. But this method of dispensing powder detergents has some disadvantages.
At the powder/screen/water interface there is exposure to high temperature, humidity, pH and electrolyte concentration. This harsh environment at the interface can deactivate enzymes or decompose peroxy bleach compounds when moistened. In addition, moisture levels would rise in the remaining suspended powder causing hydration interactions in the entire mass of the powder. By the time that the powder at the top of the mass has worked its way down to the screen and has been dissolved, some or all of its activity has dissipated.
One advantage of liquid detergents is the ease of handling because liquids can be automatically pumped or dispensed directly to their final use application. The liquid detergents can also be made into a highly concentrated intermediate aqueous solution which is subsequently flushed/diluted to its proper final use application solution. Liquid detergents are generally more rapidly soluble than powder detergents with the same or comparable active ingredients. Liquid detergents can use higher levels of some surfactants that would cause powders to cake if used at similar levels.
Almost all liquid detergents have the disadvantage that they are diluted with water, so larger volumes and weights have to be shipped, stored and used to accomplish the equivalent cleaning as a highly concentrated powder. Also, liquid detergents cannot tolerate high concentration of organic surfactants with dissolved inorganic builders and sequestering agents with all the ingredients remaining homogenous throughout its shipping and storage. Many liquid detergents utilize high concentrations of corrosive chemicals which easily spill or splatter on users causing chemical burns, blindness or discomfort. Liquids can be corrosive to their dispensing equipment by virtue of the caustic alkali being incompatible with pump parts or delivery tubing.
The ingredients within liquids interact because the ingredient molecules are mobile. These interactions can precipitate or irreversibly inactivate some of the active ingredients upon storage. For example, enzymes are not compatible with strong sequestering, chelating or calcium precipitating agents for long-term storage stability in aqueous liquid compositions. Enzyme activity decreases if the enzymes are stored in an aqueous detergent product containing high pH, strong oxidizing agents or strong sequestering or chelating agents such as phosphates, carbonates, aminocarboxylates, polyacrylates or phosphonates.
Liquids, for the most part, do not allow a stable, homogeneous solution of surfactants, builders, sequestrants and oxygen bleach source in a compatible stable product with long term storage stability. Liquid products in the marketplace do not have a stable combination of enzyme or peroxy bleach with all of the other components of an effective cleaning system. Several different products are required because the components of the liquid products are not compatible if mixed in one product.
Attempts have been made to stabilize liquid detergent compositions. U.S. Pat. No. 4,318,818 to Letton et al. describes a stabilized aqueous enzyme composition having calcium ions, a pH between 6.5 and 10, a low molecular weight alcohol and a low molecular weight carboxylic acid salt which together act to stabilize the enzyme. U.S. Pat. Nos. 4,537,706 and 4,537,707 to Severson, Jr. disclose the use of boric acid together with calcium ions and formate to stabilize enzymes in liquid detergents. These compositions show increased enzyme stability, but they still show enzyme degradation over periods of many weeks when stored at elevated temperatures (100xc2x0 F.-120xc2x0 F.).
Similar efforts have been made to stabilize bleach in liquid detergents. U.S. Pat. No. 4,430,236 to Pranks describes a liquid detergent containing a hydrogen peroxide bleach that is relatively stable at room temperature over a period of months. U.S. Pat. No. 4,507,219 to Hughes focuses on improved stability of a chlorine bleach in a liquid detergent. These compositions contain low concentrations of alkanolamines to stabilize the chlorine bleach. Careful blending is required to achieve a product that remains isotropic and stable. As a result of these efforts, some combination liquid products exist but none with the attributes of having alkaline builders, high levels of surfactants, high levels of water conditioning/sequestering/chelating agents, enzymes and oxygen bleach all in one product which is easily, safely and accurately dispensed into a laundry machine, or hard surface cleaning apparatus.
As a result of these compatibility problems, liquid products are often dispensed as several products to be mixed in the final use solution at the ratio desired and at the time needed for the desired result. For example, a liquid highly alkaline laundry builder product is pumped by a dispenser into the wash cycle of a laundry washing operation. At the same time, a second liquid product containing surfactants and enzymes is pumped into the washer. In subsequent steps in the washing cycle, a bleaching agent may be added to remove stains and enhance the color or whiteness of the fabrics.
Because of the difficulties with both powder detergents and liquid detergents, solids offer an attractive alternative. For example, solids can be dispensed from inverted containers without suffering the same problems as powders since a wire screen is not needed. Powders by their nature have very large surface areas susceptible to humidity. Solid cast detergent capsules improve this situation because the solid remains intact with a small surface area as the solid is selectively dissolved to release just enough detergent for the particular job. The only surface of the detergent susceptible to the effects of moisture or humidity is the surface exposed to water which is dissolved at the time of the next utilization.
Limited types of solid detergents have been used. U.S. Pat. No. 4,861,518 to Morganson et al. divulges a solid floor cleaner that is specifically formulated not to form a film after use. U.S. Pat. No. 5,397,506 focuses on an improved fat removing solid cleaner that contains a C12-18 alkyl dimethylamine oxide surfactant. U.S. Pat. No. Re. 32,818 to Fernholz et al. discloses a cast solid detergent containing 30 to 60% by weight alkali metal hydroxide that is hydrated. The detergent can also contain a chlorine source and a defoamer. U.S. Pat. No. Re. 32,763 claims corresponding methods of producing these solid detergents based on alkali metal hydroxide. Another alkaline based solid detergent is discussed in U.S. Pat. No. 5,340,501 to Steindorf. While these types of products have a limited surface area for interactions with water and humidity, they do not contain enzymes or oxygen bleach sources.
The detergent composition within the invention is unique in that it incorporates many of the advantages of free flowing powder or granular, and pumpable liquid detergents in one product and eliminates the disadvantages of each. The solid detergent will contain either an active enzyme, a peroxide bleach or both. The enzyme or peroxide will be relatively stable upon long storage of the solid detergent.
This invention consists of a solid mass which is essentially homogeneous on the scale of quantities used in any typical application for the detergent. In other words, while the solid may not be a homogeneous solid mixture on a microscopic level, any granules will be dispersed to form an effectively uniform mass for any practical applications. The detergent composition can contain a nonionic surfactant, an anionic surfactant, an alkaline builder and a metal sequestering agent. The total surfactant concentration will generally range from greater than 30 to less than 99 percent by weight of the detergent composition.
The surfactants are melted to form a liquefied mass, then other active detergent ingredients are added to the liquid mass. Care must be taken in the order of addition and in the temperature at which each component is added to insure stability and effectiveness of the enzyme components, the oxygen bleach source, i.e., peroxide, and to prevent adverse chemical interactions among the ingredients. Any peroxides and enzymes are added near the end of the production procedure after the detergent solution has cooled to some extent. When all of the components have been added and mixed to a now thick, effectively homogeneous suspension/dispersion, the product is removed from the mixing vessel and poured into jars, plastic or fiber containers or poured into molds where it cools below its melting point and solidifies.
If the solid mass is in a container, it can be utilized by spraying water on the exposed surface of the product where it dissolves in the water and is drained, pumped or injected to its final use application. Alternatively, if the detergent is poured into molds, the block (cake, puck, brick) can be added directly to water as in a bucket or laundry machine or dissolved in water in a receptacle where it is then transferred to the final application.